Multi-wavelength intravenous optical sensors are used for measuring saturation of venous oxygen (“SvO2”) within humans and other animals. An example SvO2 sensor projects two or more wavelengths of light into surrounding blood and measures the reflected light using a photodiode, separated from the light sources by an opaque barrier. The intensities of reflected light are combined into one or more ratios and oxygen saturation is extrapolated using an appropriate equation. Another type of SvO2 sensor having an additional light source with the same wavelength as one of the light sources used for SvO2 measurement allows for the sensor to also measure hematocrit.
Since the SvO2 sensor resides in the bloodstream, the sensor is susceptible to the variations in the optical properties of the blood that may result from cardiac activity and respiration. Additionally, pulsatile blood flow, which accompanies regular contractions of the heart can have a strong effect on the signal.
What are needed are methods of accurately processing venous oxygen saturation and hematocrit information in an implantable sensor.